Checking Date of Birth is correct on VM?

Can anyone point me in the right direction please?

I renewed my VM contract a few weeks ago and was given an O2 sim but I have failed to link my O2 account and VM account since. I'm stuck on the page where you enter date of birth and postcode.

I'm just off the phone with O2 and all the details are correct their end and have suggested checking on my virgin account whether my date of birth is correct. I can't see anywhere on my account (web or app) that allows me to check my DOB.

I'm slowly losing the plot here and cannot port my number to O2 until I have a linked account so I can see all the O2 details! Hope someone can help, thanks.